Materials used in dental applications have several desirable structural properties. They are formable into a desired shape, yet become sufficiently strong when cured. The aesthetic properties of dental materials are also important. Composite materials, such as those having a filler component and a resin component, have been found to be useful in dental applications.
Air bubbles typically become trapped in the composite material during mixing of the composite material and in loading the material into a container or delivery device. The incorporation of gas bubbles into a formable material can create both structural and aesthetic problems. Once the material is solidified, the gas bubbles form pores in the solid. These pores can reduce the structural integrity of the final product. If the pores are visible, they can also reduce the aesthetic appeal of the product.
In dental materials, the presence of pores can weaken the final dental product, causing a greater tendency for the material to crack. Pores can also cause problems when polishing the dental product. Polishing into a pore will result in a ridge or groove in the surface of the product. In addition, if large enough, the pores can be visible in the dental product, which is often translucent. Visible pores in dental materials can be objectionable to patients.
The gas incorporated into a formable material can be removed by certain methods known to the art, including centrifuging. However these prior art methods have disadvantages. Centrifuging is time consuming and can result in the separation of different components of a material. For example, when dental composite materials are centrifuged, the resin component of the composite can separate from the filler component. Centrifuging results in the pressure being applied in a non-uniform manner. The pressure exerted on a particular sample, and within the sample itself, will vary depending on the location of the sample in the centrifuge. Also, centrifuging does not address the problem of air bubbles incorporated into the composite material while loading the material into a container or delivery device. Composite materials are often provided to a dentist in a syringe.
Another method of removing air bubbles is suggested in U.S. Pat. No. 5,328,262. In this method, bone cement is subjected to a partial vacuum during the mixing process in order to reduce its porosity. The need for a partial vacuum in the manufacturing process increases the time and expense of producing the material. Furthermore, this method does not eliminate air bubbles incorporated into the material while loading it into a container.
Thus, there exists in the art a need for a simple and expedient way to reduce or eliminate the number and size of gas bubbles in a formable material, especially once the material has been placed in a container. In particular there is a need to reduce the amount of air bubbles in a composite material contained in a syringe.